1. Field of the Invention
The present invention is directed to irregularly shaped to spherically shaped compacted particles containing insecticidal phosphoroamidothioates and to methods for manufacturing and using the compacted particles. In particular, the present invention is directed to chemically stable, irregularly shaped to spherically shaped, compacted particles of insecticidal phosphoroamidothioates which contain ammonium sulfate. The present invention is also directed to methods for manufacturing compacted particles containing insecticidal phosphoroamidothioates and ammonium sulfate and for killing insects through the use of such particles.
2. State of the Art
Insecticidal compositions in various forms have been developed for diverse applications. The method of preparation of the insecticidal composition is largely determined by the physical and chemical nature of the insecticide and the intended use and method of application of the insecticide to the area to be treated.
Certain phosphoroamidothioates and phosphoroamidodithioates ("phosphoroamidothioates") are known in the art as having excellent insecticidal activity against a variety of insects and in a variety of environments. A particularly important commercial insecticide within these classes of compounds is the insecticide acephate (generic name) or Orthene.RTM. (tradename), which can be systemically taken up by a plant so that insects which feed and/or live on the plant are killed, in addition to those insects which directly ingest or are contacted by the insecticide. Acephate and related compounds are described in U.S. Pat. Nos. 3,716,600, 3,845,172 and 3,914,417, which disclose that in addition to their insecticidal properties, the compounds possess very low mammalian toxicity. Orthene.RTM. is commercially produced as a technical grade chemical of about 97 to 99.5% purity.
One method of formulating technical grade phosphoroamidothioates for commercial use is to mix the technical grade powder with an anti-caking agent, such as fumed silica, and a wetting agent. The wetting agent is utilized to wet the insecticide and the anti-caking agent, and the anti-caking agent is used to prevent agglomeration of the insecticide in its container. This formulation of insecticide can be applied to crops as a spray solution or as a dust.
The use of phosphoroamidothioates as powders allows for relatively high concentrations of insecticide to be applied to a treatment area, but the powder application suffers from various disadvantages. First, the finely divided particles of active spray may be carried by air currents into areas where harmful effects may occur. In addition, it is difficult to apply sprays or dusts to the soil surface or to lower areas of plants when dense foliage must be penetrated. Also, the powder has a bad odor. Additionally, in its powder form, it becomes airborne easily, and it is perceived as a health hazard. Finally, powdered phosphoroamidothioates suffer from chemical stability problems due to hydrolytic and catalytic driven degradation, which shortens the shelf life of the powdered insecticide.
While the use of acephate in granular form (e.g., pellets) would overcome some of the inherent difficulties involved in using sprays or dusts, granular formulations suffer from various problems.
One problem in granular compositions is the presence of dry additives and processing aids such as diluents, lubricants, flowability agents, surfactants, etc., which have been determined to aggravate the chemical stability problems of insecticidal phosphoroamidothioates. In turn, the lack of chemical stability for granular insecticidal phosphoroamidothioates interferes with the commercial feasibility of such formulations.
In addition, and importantly, binders have been used to make granular insecticidal phosphoroamidothioates by pellet or adhesion technologies. However, binders add to product cost, adversely affect the chemical stability of insecticidal phosphoroamidothioates and cause problems in processing. Also, granules containing binders can have problems with water insolubility, thereby limiting their use to direct application (placing the granules on or around each plant), which can be impractical for some commercial farming ventures.
Furthermore, methods such as pan granulation and extrusion (pelletizing), which have been used to make granules, have adverse effects on insecticidal phosphoroamidothioates like Orthene.RTM..
Pan granulation employs water, and the granules which are initially produced contain a significant amount of water. As a result, a dryer is used to remove the water from the granules. However, Orthene.RTM. degrades in water and is heat-sensitive, so the use of pan granulation is disadvantageous for producing Orthene.RTM. formulations.
In regard to pelletization processes, U.S. Pat. Nos. 5,075,058 and 5,100,667 describe processes for pelletizing formulations containing insecticides such as phosphoroamidothioates. In particular, U.S. Pat. No. 5,075,058 discloses a process for forming pellets by extruding a mixture of Orthene.RTM., a second active ingredient, and optional components such as a limited amount of ammonium sulfate, and U.S. Pat. No. 5,100,667 exemplifies a process for forming pellets of Orthene.RTM. alone or in combination with a surfactant and ammonium sulfate using a pellet mill. However, pellet mills or extruders used to form pellets from mixtures containing Orthene.RTM. can generate heat. As noted above, Orthene.RTM. is heat-sensitive, so pelletizing is disadvantageous for producing Orthene.RTM. formulations. Also, extruded or pellet forms typically produce regularly or cylindrically shaped granules which are difficult to apply directly to the ground with conventional granule application equipment. Further, U.S. Pat. Nos. 5,075,058 and 5,100,667 neither teach nor suggest that formulations which contain effectively only insecticidal phosphoroamidothioates and ammonium sulfate have enhanced chemical stability.
Thus, there is a need in the art for low cost, highly effective, chemically stable insecticidal phosphoroamidothioate granular formulations and for processes for manufacturing the same.